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Citing study results in mice, researchers at the Northwestern University Feinberg School of Medicine reported for the first time that the form of vitamin E found primarily in food (gamma‑tocopherol) increased lung inflammation in induced asthma, while the form of vitamin E found primarily in dietary supplements (alpha‑tocopherol) reduced inflammation. The study, supported in part by NCCAM and published in the Journal of Immunology, has implications for understanding why asthma rates have increased during the last 40 years.

The researchers gave mice 2 mg per day of alpha‑tocopherol, gamma‑tocopherol, a combination of 2 mg each of alpha‑tocopherol and gamma‑tocopherol, or placebo (castor oil) for 21 days. They then measured the mice's tocopherol levels and inflammation. The researchers found that compared with placebo, alpha‑tocopherol significantly reduced inflammation while gamma‑tocopherol significantly increased inflammation. In addition, in mice that were induced with asthma, gamma‑tocopherol was shown to block the benefit of alpha‑tocopherol. The researchers also found that the mechanism by which both forms of vitamin E work involves the regulation of endothelial cell signals during leukocyte (white blood cell) recruitment—a process that occurs during inflammation. Endothelial cells line the inner walls of blood vessels.

The American diet is rich in gamma‑tocopherol found in soy and vegetable oil, and in light of this study's findings, the researchers speculated that increased consumption of gamma‑tocopherol in soy and vegetable oil may have contributed to increases in asthma prevalence. The researchers concluded that the opposing activities of the two common forms of vitamin E on inflammation found in this study are consistent with the contradictory outcomes of vitamin E on asthma in previous clinical trials. They also noted that the information gained from this study could have a significant impact on designing and interpreting future clinical studies on vitamin E.